Electrodeposition of copper

ABSTRACT

BRIGHTENING COMPOSITIONS FOR COPPER PYROPHOSPHATE ELECTROPLATING SOLUTIONS COMPRISING A HETEROCYCLIC BRIGHTENER OF THE TYPE WHICH CONSISTS OF A   -N=C(-S-M)-Q-   GROUP CONTAINED IN A 5 OR 6 MEMBERED HETEROCYCLICRING SYSTEM WHERE Q REPRESENTS NITROGEN OR SULPHUR ANDM IS HYDROGEN OR A CATION (SUCH AS MERCAPTO THIAZOLES, THIADIAZOLES OR PYRIMIDINES), OR A PRECURSOR THEREOF, AD AN AUXILLIARY BRIGHTENER SELECTED FROM ARYL OR ALKARYL-SULPHONIC ACIDS HAVING AT LEAST 7 CARBON ATOMS.

United States Patent 3,729,393 ELECTRODEPOSITION OF COPPER Derek Martin Lyde, Stourbridge, England, assignor to Albright & Wilson Limited, Oldbnry, Worcestershire, England No Drawing. Original application Apr. 25, 1968, Ser. No. 724,225. Divided and this application Apr..7, 1971, Ser. No. 132,236 Claims priority, application Great Britain, May 1, 1967, 19,989/67 Int. C1. C23!) 5/18 US. Cl. 20452 R 22 Claims ABSTRACT OF THE DISCLOSURE Brightening compositions for copper pyrophosphate electroplating solutions comprising a heterocycllc brightener of the type which consists of a group contained in a 5 or 6 membered heterocyclic ring system where Q represents nitrogen or sulphur and M is hydrogen or a cation (such as mercapto thiazoles, thiadiazoles or pyrimidines), or a precursor thereof; and an auxiliary brightener selected from aryl or alkaryl-sulphonic acids having at least 7 carbon atoms.

This application is a division of application S.N. 724,225, filed Apr. 25, 1968, now abandoned.

The present invention relates to improvements in the electrodeposition of copper.

It is known to carry out the electrodeposition of copper from alkaline solutions containing an alkali metal copper pyrophosphate complex of the Formula X Cu(P O where X represents an alkali metal.

A characteristic feature of these plating solutions is that in conjunction with suitable brightening additives they may be used to form highly specular mirror bright finishes which do not require subsequent mechanical polishing. In this they differ from the conventional acid copper plating systems and from copper cyanide systems, which produce matt finishes. Brighteners used in the former solutions are intended to improve the specularity of the bright finish whereas those used in the latter systems are designed to make the matt finish more amenable to mechanical polish- Various heterocyclic compounds have been proposed as brightener additives for alkaline pyrophosphate electroplating compositions and some of these have found particular favour in the art. A group of these heterocyclic compounds is characterized by the presence of the groupmg:

( i-SH contained in a 5- or 6-membered heterocyclic ring system where Q represents a nitrogen atom (either as a=N- or -N- grouping) or a sulphur atom. Examples of these mercapto-heterocyclic compounds are described in UK. specifications Nos. 939,997; 940,282 and 1,051,150.

Some of the aforementioned specifications refer to the optional presence in the electroplating composition of other organic compounds, such as simple aliphatic or hydroxy-aliphatic carboxylic acids. These are stated, for example in specification No. 1,051,150, to improve the grain refinement of the electrodeposited material and to reduce the anodic polarisation.

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We have now discovered that it is possible to use increased concentrations of the heterocyclic brightener without loss in levelling efliciency if an auxiliary brightener is added to the composition. In an attempt to discover suitable auxiliary brighteners we have investigated the effect of adding a wide variety of organic compounds of copper pyrophosphate electrolytes containing the above-mentioned heterocyclic brightener additives. Although the majority are either ineffective or deleterious we have found several Which improve the electrolyte because they enable higher concentrations of the heterocyclic brightener to be employed and so reduce the risk of uneven plating. Thus the optimum concentration range for the heterocyclic brightener is markedly increased. This is a quite different effect for many mentioned for the lower aliphatic and hydroxy-aliphatic acids in specification No. 1,051,150, and in general the auxiliary brighteners, which we have found to be effective, possess a greater molecular weight than those compounds previously specifically mentioned for addition to copper pyrophosphate electrolytes, albeit for different purposes.

The invention therefore provides a brightening composition for use in the electrodeposition of copper from a copper pyrophosphate electrolyte, which composition comprises a primary brightener which is a mercaptoheterocyclic compound containing the group:

ii-SM contained in a 5- or 6-membered heterocyclic ring, where Q represents a nitrogen or sulphur atom and M is hydrogen or a cation such that the compound is water-soluble; and an auxiliary brightener selected from polycarboxylic or alkaryl sulphonic acids having at least 7 carbon atoms; malonic acid, 4,S-imidazole-dicarboxylic acid, imino-diacetic acid, water-soluble ammonium or alkali metal salts and anhydrides of the aforesaid acids, and hydroxyethyl cellulose.

The invention further provides an aqueous electrolyte for copper plating having dissolved therein a copper salt, an alkali metal pyrophosphate in an amount at least sufficient to form the complex X Cu(P O where X represents an alkali metal, and a minor proportion of a brightening composition according to the invention. The invention also provides a process for the electrodeposition of copper using an aqueous electrolyte of the invention.

The heterocyclic brighteners for present use are examplified: by the mercapto-thiazole compounds described in specification No. 940,282, for example 2-mercapto-1, 3- thiazole and Z-mercapto-benthiazole; by the Z-mercapto- 1, 3,4-thiadiazole compounds described in specification No. 939,997, for example 2,5-dimercapto-1,3,4-thiadiazole, 2- mercapto-S-methylmercapto-1,3,4-thiadiazole and 2- mer capto-S-n-butylmercapto-1,3,4-thiadiazole; and by the 2- mercapto-iminazole and Z-mercapto pyrimidines described in specification No. 1,051,150, for example Z-mercapto-lmethyliminazole, Z-mercaptopyrimidine, 6-hydroXy-2 mercaptopyrimidine and 6-hydroxy-2-mercapto-4-methylpyrimidine. Also included among the classes of brighteners are precursors of the compounds described above. By precursor is meant herein a compound which when dissolved in the copper pyrophosphate electrolyte provides in solution a compound containing the structure(II). For example there may be used heterocyclic disulphides containing the grouping:

-Q Q- (III) The auxiliary brighteners for present use are for the most part acids which will normally be used as sodium, potassium or ammonium salts. There can be particularly mentioned the alkaryl sulphonates wherein the salt has less than carbon atoms in each alkyl chain and preferably less than 5 aliphatic carbon atoms per sulphonate group. Alkaryl sulphonates with longer alkyl groups generally are insufiiciently efiective to be of commercial value for present purposes. Suitable salts include potassium toluene sulphonate, sodium xylene sulphonate, salts of sulphonated naphthalene-formaldehyde condensates, for example methylene bis-(naphthalene-sulphonates), and salts of sulphonated polystyrenes.

There may also be used, usually in the form of watersoluble salts, organic diand polycarboxylic acids or anhydrides thereof having more than 7 carbon atoms. As examples of these compounds there can be mentioned suberic acid, azelaic acid, and sebacic acid as well as adducts of the type formed when a dienophilic carboxylic acid such as maleic anhydride is condensed with a conjugally unsaturated hydrocarbon such as polyiso-butylene, for example the alkylor alkenyl-substituted succinic acids and anhydrides wherein the alkyl or alkenyl group contains from 30-150 carbon atoms.

Normally the heterocyclic brightening agent is employed in a proportion of at least 0.001 gram per litre of the total weight of electrolyte and preferably from 1 to mg. per litre. The optimum concentration may vary from 2 to 4 mg. per litre depending upon the nature of the auxiliary brightener present. Normally the auxiliary brightener is employed in a proportion of from 1 p.p.m. to saturation, preferably from 2 to 100 p.p.m., for example 3 to 6 p.p.m.

It is preferred that the copper plating electrolytes of the invention have a similar constitution with respect to the concentration of copper salt and pyrophosphate as those conventionally employed, for example as described in the above-mentioned specifications. These electrolytes may contain other additives that are conventionally em ployed in this type of electrolyte in addition to the heterocyclic brighteners. The electrolyte may be employed for plating metal articles in accordance with known procedures.

The invention is illustrated by the following examples wherein there were employed electrolytes of the following constitution:

Copper pyrophosphate 94 g./l., potassium pyrophosphate 300 g./l., ammonia 1 g./l., primary brightener as specified 2 p.p.m. Standard solutions were made by using 3 heterocyclic brighteners, namely 2,S-dimercapto-l,3,4- thiadiazole, 2-mercaptobenzimidazole and Z-mercaptobenzthiazole. The solutions were obtained at a pH of 8.8 at a temperature of 55 C. Plating was carried out on brass panels with a current density of 30 amps per sq. ft. under air agitation.

Tests were repeated wth the three standard electrolytes containing the following auxiliary brighteners at a concentration of 10 p.p.m.;

In each example the auxiliary brightener provided improved brightening and levelling action without skip plating.

We claim:

1. An improved process (for electrodepositing copper from an aqueous copper pyrophosphate electrolyte wherein copper is electrodeposited from electrolyte consisting essentially of an alkaline aqueous solution containing dissolved therein a copper salt and an alkali metal pyrophosphate in an amount at least sufficient to form the complex salt X Cu(P O and from one part per million to saturation of a known heterocyclic brightening additive selected from mercaptothiazoles, mercaptobenzthiazoles, mercaptothiadiazoles, mercaptoiminazoles and mercaptopyrimidines, the improvement comprising admixing in said electrolyte between two part per million and saturations of an auxiliary brightener selected from (i) alkylaryl sulphonic acids having at least 7 carbon atoms and containing less than 5 carbon atoms in each alkyl chain and less than five aliphatic carbon atoms per sulphonate group, (ii) vinyl benzene sulphonate, (iii) naphthalene trisulphonate, and (iv) polystyrene sulphonate.

2. A process according to claim 1 wherein the electrolyte contains from l to 10 parts per million of the heterocyclic brightener.

3. A process according to claim 1 wherein the electrolyte contains from 2 to 4 parts per million of the heterocyclic brightener.

4. A process according to claim 1 wherein the copper salt is copper pyrophosphate and the alkali metal pyrophosphate is potassium pyrophosphate.

5. A process according to claim 1 wherein the auxiliary brightener is sodium xylene sulphonate.

6. A process according to claim 1 wherein the auxiliary brightener is sodium toluene sulphonate.

"7. A process according to claim 1 wherein the auxiliary brightener is naphthalene trisulphonate.

8. A process according to claim 1 wherein the auxiliary brightener is vinyl benzene sulphonate.

9. A process according to claim 1 wherein the auxiliary brightener is methylene bisnaphthylene sulphonate.

'10. A process according to claim 1 wherein the auxil iary brightener is added in a concentration of from 1 to parts per million.

11. A process according to claim 1 wherein the auxiliary brightner is added in a concentration of from 2 to 4 parts per million.

12. An improved copper pyrophosphate electroplating electrolyte consisting essentially of an alkaline aqueous solution containing dissolved therein a copper salt and an alkali metal pyrophosphate in an amount at least sufi'icient to form the complex salt X Cu(P O and from one part per million to saturation of a known heterocyclic brightening additive selected from mercaptothiazoles, mercaptobenzthiazoles, mercaptothiadiazoles, mercaptoiminazoles and mercapto-pyrimidines, the improvement wherein said electrolyte also contains an auxiliary brightener selected from (i) alkylaryl sulphonic acids having at least 7 carbon atoms and containing less than 5 carbon atoms in each alkyl chain and less than five aliphatic carbon atoms per sulphonate group, (ii) vinylbenzene sulphonate, (iii) naphthalene trisulphonate, and (iv) polystyrene sulphonate, in a concentration of from 2 parts per million to saturation.

13. An electrolyte according to claim 12 wherein the heterocyclic brightner is present in a concentration of from =1 to 10 parts per million.

14. An electrolyte according to claim 12 wherein the heterocyclic brightner is present in a concentration of of from 2 to 4 parts per million.

I15. An electrolyte according to claim 12 wherein the copper salt is copper pyrophosphate and the alkali metal pyrophosphate is potassium pyrophosphate.

16. An electrolyte according to claim 12 containing from 2 to 100 parts per million of the auxiliary brightener.

17. An additive for use in aqueous copper pyrophosphate electroplating solutions consisting essentially of (a) a known heterocyclic brightening additive selected from mercaptothiazoles, mercaptobenzthiazoles, mercaptothiadiazoles, mercaptoiminazoles, and mercaptopyrimidines and (b) an auxiliary brightener selected from (i) alkyaryl sulphonic acids having at least 7 carbon atoms, and contining less than 5 carbon atoms in each alkyl chain and less than five aliphatic carbon atoms per sulphonate group, (ii) vinylbenzene sulphonate, (iii) naphthalene trisulphonate, and (iv) polystyrene sulphonate.

18. An additive according to claim 17 wherein the auxiliary brightner is sodium xylene sulphonate.

19. An additive according to claim 17 wherein the auxiliary brightner is sodium toluene sulphonate.

20. An additive according to claim 17 wherein the auxiliary brightener is sodium naphthalene trisulphonate.

21. An additive according to claim 17 wherein the auxiliary brightner is potassium vinyl benzene sulphonate.

22. An additive according to claim 17 wherein the auxiliary brightner is sodium methylene bisnaphthylene sulphonate.

References Cited UNITED STATES PATENTS 2,090,049 8/1937 Hull 204- Y 2,195,409 4/ 1940 Flett 20446 2,437,865 3/1948 Stareck 20452 R 2,700,019 1/1955 Jernstedt 204-52 R 3,161,575 12/1964 Wells et a1. 20452 3,341,433 9/1967 Passal 20449 2,250,556 7/11941 Stareck 20452 R 3,296,101 1/ 1967 Crain 20444 3,373,095 3/1968 Abbott 20452 R FOREIGN PATENTS 774,424 5/1957 Great Britain 20452 940,282 10/ 1963 Great Britain 20452 1,051,150 12/ 1966 Great Britain 20452 FREDERICK C. EDMUNDSON, Primary Examiner 

